Geminiviruses present the most serious disease problem in many vegetable crops in tropical and subtropical regions. Brown et al. (1992) Plant Disease, 76:220-225. Major epidemics of geminivirus infections of beans and tomatoes have recently occurred in Florida, the Caribbean Basin, Mexico, Central America, Southern Europe, the Jordan Valley and Turkey. Unfortunately, traditional breeding methods have failed to produce cultivars with significant levels of resistance to geminiviruses.
Geminiviruses are characterized by a covalently closed circular single-stranded DNA genome (css-DNA) that infect both monocotyledonous and dicotyledonous plants. These viruses occur as twinned ("geminate") icosahedral particles. Geminiviruses are traditionally classified into two major subgroups, based on their insect vector, host range, and genome organization. Padidam et al. (1995) J Gen. Virol. 76:249-263. The first subgroup includes leaf-hopper transmitted viruses that infect mainly monocotyledonous plants and possess a single monopartite genome. The second subgroup includes viruses that are transmitted by a whitefly (Bemisia tabaci), infect dicotyledonous plants and possess a bipartite genome. A third subgroup has also been discovered and includes geminiviruses that have properties intermediate between the previously described two subgroups.
For example, the tomato yellow leaf curl virus (TYLCV) is one of the most devastating virus diseases of cultivated tomato (Lycopersicon esculentum). Tomato yellow leaf curl virus is a subgroup III whitefly transmitted geminivirus that contains a single monopartite genome. Navot, N. et al., (1991) Virology, 151-161. However, the cloning of a TYLCV-like whitefly-transmitted geminivirus with a bipartite genome from Thailand has also been reported. See Rochester, D. E., et al., (1990) Virology, 520-526.
The TYLCV genome contains 6 open reading frames. Open reading frames, V1 and V2, are located on the virion (plus) strand. The four remaining open reading frames, C 1, C2, C3 and C4, are located on the complementary (minus) strand. The C2 open reading frame partially overlaps with the C1 and C3 open reading frames; C4 is completely covered by the overlapping C1 gene. The C1 open reading frame is sometimes referred to as AC1.
Complete or partial sequence data are available for several TYLCV isolates. For example, the genome of an Israeli isolate of TYLCV has been cloned and sequenced. Navot, N. et al., (1991) Virology, 151-161. Sequence data are also available for TYLCV isolates from Sardinia. Kheyr-Pour, A., et al., (1991) Nucl. Acids Res., 19:6763-6769. The Australian isolate of TYLCV was disclosed in Dry et al. (1993) J Gen. Virol. 74:147-151. The sequence of the Thailand isolate was published by Rochester (1994) J. Gen. Virol. 75:477-485. An additional Thailand isolate was disclosed by S. Attathom to Padidam et al. (1995) J. Gen. Virol. 76:249-263. Egyptian and Sicilian isolates were similarly disclosed to Padidam et al. (1995) J. Gen. Virol. 76:249-263 by N. Abdallah and G. Accotto, respectively.
The object of the present invention is to produce transgenic plants that are resistant to geminivirus infection, such as, but not limited to, infection by the tomato yellow leaf curl virus. An additional object of the present invention is to provide methods for creating transgenic plants resistant to geminivirus infection.